The present invention is directed to a tool bit to be inserted into a chuck in a manually operated tool used for chisel-cutting and/or percussion drilling. The tool bit has a shank section and a working section with the end region in the shank section remote from the working section containing first and second faces effective in the axial and circumferential directions. In addition, the shank section has radially extending entrainment faces located in a part of the shank section projecting radially outwardly from the outer surface of the shank section containing the first and second faces. The entrainment faces are spaced, relative to the first and second faces, toward the working section of the tool bit.
Known tools of the above type usually have faces acting in circumferential direction for transmitting torque and other faces acting in the axial direction for the axial retention of the tool bit in the chuck of a hand-held or manually operated tool. It is common to locate the faces acting in the circumferential direction in the driving or entrainment grooves which are open towards the free end of the shank section.
The tool bit chuck for the above-mentioned tool bits has a receiving region usually containing entrainment strips forming counterfaces for the faces acting in the circumferential direction. It is conventional for axial retention to provide grooves closed at the ends extending transversely of the axial direction and located in the shank section of the tool bit with radially displaceable locking elements in the chuck for engagement in the closed ended grooves. Accordingly, it is necessary to disengage or shift the locking elements from the grooves in the shank section to remove the tool bit from the chuck. Tool bits as well as a tool bit chuck of this type are known, such as disclosed in DE-PS 25 51 125.
While the faces of the tool bit acting in the axial direction do not have to meet any special requirements, since they are necessary only for retaining the tool bit in the chuck, the faces acting in the circumferential direction have to meet very considerable requirements, because the torque which they transmit may be very high. As a result of the torque to be transmitted, the faces acting in circumferential direction require appropriate generous dimensions. Since the size of the shank section is limited, the dimensions of the faces acting in the circumferential direction are also limited, especially since such dimensions involve a cross-sectional weakening of the shank section. All of these limiting values regarding the dimension of the faces acting in the circumferential direction entail, in view of the torque to be transmitted especially with tool bits having larger diameter in the working region, excessive wear of the faces leading to premature failure of the tool bits.
To afford additional faces effective in the circumferential direction, a tool bit with projections is known from DE-OS 38 43465, with the projections located closer to the working section of the tool bit than the other faces. These projections protruding beyond the diameter of the shank section form entrainment faces cooperating with matching counterfaces on the tool bit chuck known from the above patent publication. These entrainment faces, however, cannot meet the requirements for sufficiently reducing the load acting on the faces effective in the circumferential direction at the occurring high torques. The reason for this is, on one hand, that the entrainment faces protrude directly from the diameter of the shank section, so that the moment to be carried is too small and, on the other hand, that the radial dimension is too small and leads to entrainment faces which are also too small.